Engine idles fine, but bogs/hesitates at low RPMs?

[BlackStraw]

Hi,

Unfortunately not a 4WD, but I've found this board has some of the best general information on the 3A engine and was hoping a member might be able to give me some ideas of what to look at.

I have a 1986 Tercel hatchback, automatic trans.....starts fine, idles smoothly....If I put the trans in "Drive" and let it creep forward without touching the gas, also runs smooth. But it stumbles a bit if I just barely touch the gas pedal, up to maybe up a quarter distance to the floor. As soon as I press the gas more than a quarter, it accelerates smoothly and runs great at higher RPMs/highway speeds. It's annoying for low-speed manoevering, like in a parking lot or backing up. Is this likely to be a vacuum leak? Something in the carb that needs adjusting or cleaning? Seems fairly consistent between engine cold and hot, just a narrow range of the gas pedal which causes sputtering.

[irowiki]

Could be a leaky AAP. I'd see if it is leaking and cap it off it so.

Maybe up the idle just a tad.

[BlackStraw]

Okay thanks I'll try that....it already idles a bit high for my liking, I'd prefer not to turn it any higher.

[irowiki]

What does it idle at now?

I had to turn my auto T4 from the factory of like 700 to like 1100 for it to be happy at all.

[BlackStraw]

There's no tach so I'm just guessing by ear, but perhaps between 1100 and 1300? No problem idling low when I turn the screw down, but then it almost stalled everytime I touched the gas, so turned it back up again so that it merely sputters again going through that range. And again no hestitation or issues above 1800rpm(?) or highway speeds.

[dlb]

sounds like a vacuum leak to me.

[Petros]

welcome to the forum,

I would look for a vacuum leak, the AAP is also a good thing to check, it also might just need spark plugs and/or spark plug wires. I got an auto trans T4wd cheap that acted this way, the local repair shop kept trying wacky things to "fix it", owner thought it might have needed a carb rebuild and did not want to spend the money on it. I got it, took all their crap off the shop installed and looked for vac leak, adjusted all the linkage properly, and has been driving well for two years now (I gave it to my daughter to drive, still going strong).

[rrpierce]

ok, I give up, what is "AAP"?

[Notmikeb]

Auxiliary Accelerator Pump. It's a small diaphragm on the front left of your carb. There is a vacuum line running to it. If the rubber diaphragm is ruptured, gas will end up in the vacuum line causing a vacuum leak and a slightly over rich condition. Pull the line and see if there is gas in it. You can also (carefully) suck on the line to see if it holds vacuum. If it is bad, just disconnect that line and cap off both ends as it is not 100% necessary just improves cold driving response slightly but does nothing once warmed up.